Polishing composition including an inhibitor of tungsten etching

ABSTRACT

A chemical mechanical polishing composition comprising a composition capable of etching tungsten and at least one inhibitor of tungsten etching and methods for using the composition to polish tungsten containing substrates.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/901,803, filed Jul. 28, 1997, now U.S. Pat. No. 6,083,419.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a chemical mechanical polishing (CMP)composition including a compound capable of etching tungsten and atleast one inhibitor of tungsten etching. The polishing composition isuseful alone or in combination with other chemicals and abrasives forpolishing metal layers and thin-films associated with semiconductormanufacturing where one of the layers or films is comprised of tungsten.

2. Description of the Related Art

Integrated circuits are made up of millions of active devices formed inor on a silicon substrate. The active devices, which are initiallyisolated from one another, are united to form functional circuits andcomponents. The devices are interconnected through the use of well-knownmultilevel interconnections. Interconnection structures normally have afirst layer of metallization, an interconnection layer, a second levelof metallization, and sometimes a third and subsequent levels ofmetallization. Interlevel dielectrics such as doped and undoped silicondioxide (SiO₂), are used to electrically isolate the different levels ofmetallization in a silicon substrate or well. The electrical connectionsbetween different interconnection levels are made through the use ofmetallized vias and in particular tungsten vias. U.S. Pat. No.4,789,648, which is incorporated herein by reference, describes a methodfor preparing multiple metallized layers and metallized vias ininsulator films. In a similar manner, metal contacts are used to formelectrical connections between interconnection levels and devices formedin a well. The metal vias and contacts are generally filled withtungsten and generally employ an adhesion layer such as titanium nitride(TiN) and/or titanium to adhere a metal layer such as a tungsten metallayer to SiO₂.

In one semiconductor manufacturing process, metallized or contacts areformed by a blanket tungsten deposition followed by a chemicalmechanical polish (CMP) step. In a typical process, via holes are etchedthrough an interlevel dielectric (ILD) to interconnection lines or to asemiconductor substrate. Next, a thin adhesion layer such as titaniumnitride and/or titanium is generally formed over the ILD and is directedinto the etched via hole. Then, a tungsten film is blanket depositedover the adhesion layer and into the via. The deposition is continueduntil the via hole is filled with tungsten. Finally, the excess tungstenis removed by chemical mechanical polishing (CMP) to form metal vias.Processes for manufacturing and/or CMP of ILD's are disclosed in U.S.Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.

In a typical chemical mechanical polishing process, the substrate isplaced in direct contact with a rotating polishing pad. A carrierapplies pressure against the backside of the substrate. During thepolishing process, the pad and table are rotated while a downward forceis maintained against the substrate back. An abrasive and chemicallyreactive solution, commonly referred to as a "slurry" is deposited ontothe pad during polishing. The slurry initiates the polishing process bychemically reacting with the film being polished. The polishing processis facilitated by the rotational movement of the pad relative to thesubstrate as slurry is provided to the wafer/pad interface. Polishing iscontinued in this manner until the desired film on the insulator isremoved.

The slurry composition is an important factor in the CMP step. Dependingon the choice of the oxidizing agent, the abrasive, and other usefuladditives, the polishing slurry can be tailored to provide effectivepolishing of metal layers at desired polishing rates while minimizingsurface imperfections, defects, corrosion, and erosion of oxide in areaswith tungsten vias. Furthermore, the polishing slurry may be used toprovide controlled polishing selectivities to other thin-film materialsused in current integrated circuit technology such as titanium, titaniumnitride and the like.

Typically CMP polishing slurries contain an abrasive material, such assilica or alumina, suspended in an oxidizing, aqueous medium. Forexample, U.S. Pat. No. 5,244,534 to Yu et al. reports a slurrycontaining alumina, hydrogen peroxide, and either potassium or ammoniumhydroxide that is useful in removing tungsten at predictable rates withlittle removal of the underlying insulating layer. U.S. Pat. No.5,209,816 to Yu et al. discloses a slurry comprising perchloric acid,hydrogen peroxide and a solid abrasive material in an aqueous medium.U.S. Pat. No. 5,340,370 to Cadien and Feller discloses a tungstenpolishing slurry comprising approximately 0.1M potassium ferricyanide,approximately 5 weight percent silica and potassium acetate. Acetic acidis added to buffer the pH at approximately 3.5.

Most of the currently available CMP slurries contain largeconcentrations of dissolved, ionic metallic components. As a result, thepolished substrates can become contaminated by the adsorption of chargedspecies into the interlayers. These species can migrate and change theelectrical properties of the devices at gates and contacts and changethe dielectric properties of the SiO₂ layers. These changes may reducethe reliability of the integrated circuits with time. Therefore, it isdesirable to expose the wafer only to high purity chemicals with verylow concentrations of mobile metallic ions.

CMP compositions are increasingly being formulated with chemicalingredients that are capable of etching tungsten in an effort to improvethe rate at which tungsten vias are polished. However, in many cases theresulting CMP slurry compositions etch tungsten in a manner thatsolubilizes the tungsten instead of converting the surface to a softoxidized film with improved tungsten abradeability. Due to thesechemical compositions, recessing of the tungsten plug due to undesirabletungsten etching occurs. Recessed tungsten vias, where the surface ofthe tungsten is below that of the surrounding insulator surface, are aproblem because they can cause electrical contact problems to otherparts of the device. In addition, problems due to tungsten recess may becaused by the fact that the resulting nonplanarity may complicate thedeposition of metal layers on subsequent levels of the device.

Tungsten etching can also cause undesirable "keyholing" of tungstenvias. Keyholing is a phenomenon whereby a hole is etched into the centerof a tungsten via and, thereafter, the hole migrates towards the sidesof the via. Keyholing causes the same contact and filling problems asrecessing.

A new CMP composition is needed that both polishes tungsten at highrates and that does not cause undesirable tungsten plug recessing.

SUMMARY OF THE INVENTION

The present invention is directed to a chemical mechanical polishingcomposition that s capable of polishing tungsten at high rates withminimal etching and/or corrosion.

In addition, the chemical mechanical polishing composition of thisinvention is able to polish substances with tungsten layers atcontrolled rates with good trans-surface uniformity.

This invention is also a state-of-the-art chemical mechanical polishingcomposition that is able to polish a substrate including tungsten viasand damascene at very high rates to give a polished substrate that iscapable of accepting a subsequent layer of metallization withoutfilling, or contact problems caused by unacceptable recessing orkeyholing.

Furthermore, this invention is directed to methods for using thechemical mechanical polishing composition of this invention in a slurryto polish a plurality of metal layers in an integrated circuit includingtungsten layers.

In one embodiment, this invention is a chemical mechanical polishingcomposition comprising a compound that is capable of etching tungsten,and at least one inhibitor of tungsten etching.

In another embodiment, this invention is a chemical mechanical polishingcomposition including a compound that is capable of etching tungsten,and at least one inhibitor of tungsten etching, wherein the inhibitor oftungsten etching is an amino alkyl compound, a compound that formsalkylammonium ions at a solution pH less than about 9.0, and mixturesthereof.

In yet another embodiment, this invention is a chemical mechanicalpolishing slurry having a pH less than about 4.0 including from about0.5 to about 15.0 weight percent silica, from about 0.001 to about 0.2weight percent ferric nitrate, from about 1.0 to about 10.0 weightpercent hydrogen peroxide, at least one stabilizer, and from about 0.001to about 1.0. wt % glycine.

This invention is also a method for polishing a substrate including atleast one tungsten layer. The polishing method begins by admixing atleast one compound that is capable of etching tungsten, at least oneinhibitor of tungsten etching and deionized water to give a chemicalmechanical polishing composition having a pH less than 5.0, wherein thecompound capable of etching tungsten is a nitrogen containing compound.The chemical mechanical polishing composition is then applied to thesubstrate, and a pad is brought into contact with the substrate for aperiod of time sufficient to remove at least a portion of the tungstenlayer from the substrate.

DESCRIPTION OF THE CURRENT EMBODIMENT

The present invention relates to a chemical mechanical polishingcomposition that comprises a compound that is capable of etchingtungsten and at least one inhibitor of tungsten etching. The chemicalmechanical polishing composition is used to polish at least one tungstenmetal layer associated with a substrate selected from the groupincluding silicon substrates, TFT-LCD glass substrates, GaAs substrates,and other substrates associated with integrated circuits, thin films,multiple level semiconductors, and wafers. In particular, the chemicalmechanical polishing composition of this invention exhibits excellentpolishing performance when used to polish a substrate including one ormore layers of tungsten, titanium, and titanium nitride layers of asubstrate in a single step.

Before describing the details of the various preferred embodiments ofthis invention, some of the terms that are used herein will be defined.The "chemical mechanical composition" refers to the combinationcomprising a compound that is capable of etching tungsten and at leastone inhibitor of tungsten etching that may be used in conjunction withan abrasive pad to remove one or more layers of metal from a multiplelayer metallization.

The term "chemical mechanical polishing slurry" or "CMP slurry", refersto another useful product of this invention that comprises the chemicalmechanical composition of this invention and at least one abrasive. TheCMP slurry is useful for polishing a multiple level metallization whichmay include but is not limited to semi-conductor thin-films, integratedcircuit thin-films, and for polishing any other films, surfaces andsubstrates where CMP processes are useful.

One aspect of this invention is a chemical mechanical compositioncomprising a compound that is capable of etching tungsten and at leastone inhibitor of tungsten etching. The chemical mechanical compositionof this invention is useful when incorporated in a chemical mechanicalpolishing slurry to polish a metal layer including tungsten. Thecombinations disclosed herein are useful when incorporated into a CMPslurry or when used alone in conjunction with an abrasive pad to polishmetals and metal based components including tungsten, titanium, titaniumnitride, copper, aluminum, tantalum, tantalum nitride, and variousmixtures and combinations thereof.

The chemical mechanical composition of this invention includes at leastone compound that is capable of etching tungsten. The term "compoundcapable of etching tungsten" as used herein refers to a compound thatcorrodes tungsten by turning solid tungsten metal or its oxide into asoluble tungsten corrosion product. A compound that is capable ofetching tungsten may include one or more components that react withtungsten metal or its oxide to form soluble tungsten corrosion productsand/or it may refer to a composition that is applied to tungsten atcontrolled conditions, such as high pH, high temperature, high pressureor combinations thereof, that promote the conversion of tungsten metalor its oxide into soluble tungsten corrosion products.

Non-limiting examples of compounds that are capable of etching tungsteninclude oxidizing agents, fluoride containing compounds, and organicacids such as oxalic acid and malonic acid. Many oxidizing agents etchtungsten at low rates at low pH. Sometimes, composition pH can enhancethe tungsten etching rate of oxidizing agents.

The compound capable of etching tungsten of this invention may be afluoride containing additive. Fluoride containing additives useful astungsten etchants may be any known fluoride containing additives in anaqueous solution. Examples of useful fluoride containing additivesinclude fluoride salts, fluoride containing acids, fluoride polymers,and any other organic or inorganic fluoride containing additives thatreact with titanium. Aqueous compounds that are applied to tungsten attemperatures, and/or pH's that promote tungsten etching also fall withinthe definition of compounds that are capable of etching tungsten. Whencomposition application conditions are controlled to cause tungstenetching, then it is preferred that solution pH is the controlledcomposition application parameter.

The inhibitors of tungsten etching are effective at composition pH's upto about 9.0. It is preferred that the compositions of this inventionhave a pH of less than about 7.0 and most preferably less than about5.0.

The compound capable of etching tungsten may be one or more oxidizingagents. The oxidizing agent used is preferably one or more inorganic ororganic per-compounds. A per-compound as defined by Hawley's CondensedChemical Dictionary is a compound containing at least one peroxy group(--O--O--) or a compound containing an element in its highest oxidationstate. Examples of compounds containing at least one peroxy groupinclude but are not limited to hydrogen peroxide and its adducts such asurea hydrogen peroxide and percarbonates, organic peroxides such asbenzyl peroxide, peracetic acid, and di-t-butyl peroxide,monopersulfates (SO₅ ⁼), dipersulfates (S₂ O₈ ⁼), and sodium peroxide.

Examples of compounds containing an element in its highest oxidationstate include but are not limited to periodic acid, periodate salts,perbromic acid, perbromate salts, perchloric acid, perchloric salts,perboric acid, and perborate salts and permanganates. Examples ofnon-per compounds that meet the electrochemical potential requirementsinclude but are not limited to bromates, chlorates, chromates, iodates,iodic acid, and cerium (IV) compounds such as ammonium cerium nitrate.

Preferred oxidizing agents are hydrogen peroxide and its adducts such asurea hydrogen peroxide and percarbonates, organic peroxides such asbenzoyl peroxidc, peracetic acid, and di-t-butyl peroxide,monopersulfates (SO₅ ⁼), dipersulfates (S₂ O₈ ⁼), sodium peroxide, andmixtures thereof. A most preferred compound capable of etching tungstenis hydrogen peroxide.

Oxidizing agents capable of etching tungsten may be present in theoverall chemical mechanical polishing composition in an amount rangingfrom about 0.5 to about 50.0 weight percent. It is preferred that one ormore oxidizing agents is present in the polishing composition in anamount ranging from about 0.5 to about 10.0 weight percent.

Compositions of this invention include at least one inhibitor oftungsten etching. The compound inhibits the conversion of solid tungsteninto soluble tungsten compounds while at the same time allowing thecomposition to convert tungsten to a soft oxidized film that can beevenly removed by abrasion. Classes of compositions that are usefulinhibitors of tungsten etching include compounds having nitrogencontaining functional groups such as nitrogen containing heteroycles,alkyl ammonium ions, amino alkyls, amino acids. Examples of usefulcorrosion inhibitors that include nitrogen containing heterocyclefunctional groups include 2,3,5-trimethylpyrazine,2-ethyl-3,5-dimethylpyrazine, quinoxaline, acetyl pyrrole, pyridazine,histidine, pyrazine, benzimidazole and mixtures thereof.

Examples of corrosion inhibitors that include a nitrogen containingfunctional group and at least one functional group selected from thiolor sulfide functional groups include glutathione (reduced), cysteine,2-mercapato benzimidazole, cystine, thiophene, mercapato pyridineN-oxide, thiamine hydrochloride, tetraethyl thiuram disulfide,2,5-dimercapto-1,3-thiadiazole and mixtures thereof.

The term "alkyl ammonium ion" as used herein refers to nitrogencontaining compounds having functional groups that can produce alkylammonium ions in aqueous solutions. The level of alkylammonium ionsproduced in aqueous solutions including compounds with nitrogencontaining functional groups is a function of solution pH and thecompound or compounds chosen. Examples of nitrogen containing functionalgroup corrosion inhibitors that produce inhibitory amounts of alkylammonium ion functional groups at aqueous solution pH's less than 9.0include monoquat isies isostearylethylimididonium), cetyltrimethylammonium hydroxide, alkaterge E (2-heptadecenyl-4-ethyl-2 oxazoline4-methanol), aliquat 336 (tricaprylmethyl ammonium chloride), nuospet101 (4,4 dimethyloxazolidine), tetrabutylammonium hydroxide,dodecylamine, tetramethylammonium hydroxide and mixtures thereof.

Useful amino alkyl corrosion inhibitors include, for example,aminopropylsilanol, aminopropylsiloxane, dodecylamine, mixtures thereof,and synthetic and naturally occurring amino acids including, forexample, lysine, tyrosine, glutamine, glutamic acid, glycine, cystine,scrinc and glycine.

A preferred alkyl ammonium ion functional group containing inhibitor oftungsten etching is SILQUEST A-1106 silane, manufactured by OSISpecialties, Inc. SILQUEST A-1106 is a mixture of approximately 60 wt %water, approximately 30 wt % aminopropylsiloxane, and approximately 10wt % aminopropylsilanol. The aminopropylsiloxane and aminopropylsilanoleach form an inhibiting amount of corresponding alkylammonium ions at apH less than about 7. A most preferred amino alkyl corrosion inhibitoris glycine (aminoacetic acid).

The inhibitor of tungsten etching should be present in the compositionof this invention in amounts ranging from about 0.001 to about 2.0weight percent and preferably from about 0.005 to about 1.0 weightpercent, and most preferably from about 0.01 to about 0.10wt %.

The chemical mechanical composition of this invention optionallyincludes at least one catalyst. The purpose of the catalyst is totransfer electrons from the metal being oxidized to the oxidizer (oranalogously to transfer electrochemical current from the oxidizer to themetal). The catalyst or catalysts chosen may be metallic, non-metallic,or a combination thereof and the catalyst must be able to shuffleelectrons efficiently and rapidly between the oxidizer and metalsubstrate surface. Preferably, the catalyst is an iron catalyst such as,but not limited to, inorganic salts of iron, such as iron (II or III)nitrate, iron (II or III) sulfate, iron (II or III) halides, includingfluorides, chlorides, bromides, and iodides, as well as perchlorates,perbromates and periodates, and ferric organic iron (II or III)compounds such as but not limited to acetates, acetylacetonates,citrates, gluconates, malonates, oxalates, phthalates, and succinates,and mixtures thereof.

The catalyst may be present in the chemical mechanical polishingcomposition in an amount ranging from about 0.001 to about 2.0 weightpercent. It is preferred that the catalyst will be present in thechemical mechanical polishing composition in an amount ranging fromabout 0.005 to about 0.5 weight percent. It is most preferred that thecatalyst will be present in the composition in an amount ranging fromabout 0.01 to about 0.05 weight percent.

The amount of catalyst in the chemical mechanical composition of thisinvention may be varied depending upon the oxidizing agent used. Whenthe preferred oxidizing agent hydrogen peroxide is used in combinationwith a preferred catalyst such as ferric nitrate, the catalyst willpreferably be present in the composition in an amount ranging from about0.005 to about 0.20 weight percent (approximately 7 to 280 ppm Fe insolution).

The concentration ranges of catalyst in the chemical mechanicalpolishing slurry of this invention are generally reported as a weightpercent of the entire compound. The use of high molecular weight metalcontaining compounds that comprise only a small percentage by weight ofcatalyst is well within the scope of catalysts in this invention. Theterm catalyst when used herein also encompasses compounds wherein thecatalytic metal comprises less than 10% by weight of the metal in thecomposition and wherein the metal catalyst concentration in the CMPslurry is from about 2 to about 3000 ppm of the overall slurry weight.

A preferred chemical mechanical composition of this invention includeshydrogen peroxide and an iron catalyst. The preferred inhibitors oftungsten etching for this composition is glycine, aminopropylsilanol,aminopropylsiloxane, and mixtures thereof. The preferred inhibitors donot adversely effect the iron catalyst, they are relatively stable todecomposition from peroxides, and they do not significantly reducetungsten polishing rates.

The chemical mechanical composition of this invention may be combinedwith at least one abrasive to produce a CMP slurry. The abrasive istypically a metal oxide abrasive. The metal oxide abrasive may beselected from the group including alumina, titania, zirconia, germania,silica, ceria and mixtures thereof. The CMP slurry of this inventionpreferably includes from about 0.5 to about 15.0 weight percent or moreof an abrasive. It is more preferred, however, that the CMP slurry ofthis invention includes from about 1.0 to about 10.0 weight percentabrasive, and most preferably from about 1.5 to about 6.0 weight percentabrasive.

The metal oxide abrasive may be produced by any techniques known tothose skilled in the art. Metal oxide abrasives can be produced usingprocess such as sol-gel, hydrothermal or, plasma process, or byprocesses for manufacturing fumed or precipitated metal oxides.Preferably, the metal oxide is a fumed or precipitated abrasive and,more preferably it is a fumed abrasive such as fumed silica or fumedalumina. For example, the production of fumed metal oxides is awell-known process which involves the hydrolysis of suitable feedstockvapor (such as aluminum chloride for an alumina abrasive) in a flame ofhydrogen and oxygen. Molten particles of roughly spherical shapes areformed in the combustion process, the diameters of which are variedthrough process parameters. These molten spheres of alumina or similaroxide, typically referred to as primary particles, fuse with one anotherby undergoing collisions at their contact points to form branched, threedimensional chain-like aggregates. The force necessary to breakaggregates is considerable and often considered irreversible. Duringcooling and collecting, the aggregates undergo further collision thatmay result in some mechanical entanglement to form agglomerates.Agglomerates are thought to be loosely held together by van der Waalsforces and can be reversed, i.e., de-agglomerated, by proper dispersionin a suitable media.

Precipitated abrasives may be manufactured by conventional techniquessuch as by coagulation of the desired particles from an aqueous mediumunder the influence of high salt concentrations, acids or othercoagulants. The particles are filtered, washed, dried and separated fromresidues of other reaction products by conventional techniques known tothose skilled in the art.

A preferred metal oxide will have a surface area, as calculated from themethod of S. Brunauer, P. H. Emmet, and I. Teller, J. American ChemicalSociety, Volume 60, Page 309 (1938) and commonly referred to as BET,ranging from about 5 m² /g to about 430 m² /g and preferably from about30 m² /g to about 170 m² /g. Due to stringent purity requirements in theIC industry the preferred metal oxide should be of a high purity. Highpurity means that the total impurity content, from sources such as rawmaterial impurities and trace processing contaminants, is typically lessthan 1% and preferably less than 0.01% (i.e., 100 ppm).

In this preferred embodiment, the metal oxide abrasive consists of metaloxide aggregates having a size distribution less than about 1.0 micron,a mean aggregate diameter less than about 0.4 micron and a forcesufficient to repel and overcome the van der Waals forces betweenabrasive aggregates themselves. Such metal oxide abrasive has been foundto be effective in minimizing or avoiding scratching, pit marks, divotsand other surface imperfections during polishing. The aggregate sizedistribution in the present invention may be determined utilizing knowntechniques such as transmission electron microscopy (TEM). The meanaggregate diameter refers to the average equivalent spherical diameterwhen using TEM image analysis, i.e., based on the cross-sectional areaof the aggregate. By force is meant that either the surface potential orthe hydration force of the metal oxide particles must be sufficient torepel and overcome the van der Waals attractive forces between theparticles.

In another preferred embodiment, the metal oxide abrasive may consist ofdiscrete, individual metal oxide particles having a primary particlediameter less than 0.4 micron (400 nm) and a surface area ranging fromabout 10 m² /g to about 250 m² /g.

It is preferred that the metal oxide abrasive is silica having a surfacearea of from about 120 m² /g to about 200 m² /g.

Preferably, the metal oxide abrasive is incorporated into the aqueousmedium of the polishing slurry as a concentrated aqueous dispersion ofmetal oxides, which concentrated aqueous dispersion of metal oxideabrasives typically ranges from about 3% to about 45% solids, andpreferably between 10% and 20% solids. The aqueous dispersion of metaloxides may be produced utilizing conventional techniques, such as slowlyadding the metal oxide abrasive to an appropriate medium, for example,deionized water, to form a colloidal dispersion. The particles may bewashed, dried and separated from residues of other reaction products byconventional techniques known to those skilled in the art. Thedispersion is typically completed by subjecting it to high shear mixingconditions known to those skilled in the art. The pH of the slurry maybe adjusted away from the isoelectric point to maximize colloidalstability.

Other well known polishing slurry additives may be incorporated alone orin combination into the chemical mechanical polishing slurry of thisinvention. A non-inclusive list is inorganic acids, surfactants, anddispersing agents.

An optional additive which may be useful with this invention is onewhich stabilizes the inorganic or organic per compound in the presenceof a metal complex. For example, it is well known that hydrogen peroxideis not stable in the presence of many metal ions without the use ofstabilizers. For this reason, the CMP composition and slurries of thisinvention may include a stabilizer. Without the stabilizer, the optionalcatalyst and the inorganic or organic per compound may react in a mannerthat degrades the per compound rapidly over time. The addition of astabilizer to compositions of this invention reduces the effectivenessof the catalyst. Therefore the choice of the type and amount ofstabilizer added to the composition is important and has a significantimpact on CMP performance.

An additive which may be useful with this invention is one whichstabilizes the oxidizer in the presence of the metal complex. It is wellknown that hydrogen peroxide is not stable in the presence of many metalions without the use of stabilizers. For this reason, the CMPcomposition and slurries of this invention may include a stabilizer.Without the stabilizer, the catalyst and the oxidizing agent may reactin a manner that degrades the oxidizing agent rapidly over time. Theaddition of a stabilizer to compositions of this invention reduces theeffectiveness of the catalyst. Therefore the choice of the type andamount of stabilizer added to the composition is important and has asignificant impact on CMP performance.

The addition of a stabilizer to the compositions and slurries of thisinvention is presently understood to create a stabilizer/catalystcomplex that inhibits the catalyst from reacting with the oxidizingagent. For purpose of this disclosure the term "product of the mixtureof at least one catalyst having multiple oxidation states and at leastone stabilizer" refers to an admixture of both ingredients as used in acomposition and slurry whether or not the combination of ingredientsforms a complex in the end product.

Useful stabilizers include phosphoric acid, organic acids (e.g., adipic,citric, malonic, orthophthalic, and EDTA), phosphonate compounds,nitriles and other ligands which bind to the metal and reduce itsreactivity toward hydrogen peroxide decomposition and mixture thereof.The acid stabilizers may be used in their conjugate form, e.g., thecarboxylate can be used instead of the carboxylic acid. For purposes ofthis application the term "acid" as it is used to describe usefulstabilizers also means the conjugate base of the acid stabilizer. Forexample the term "adipic acid" means adipic acid and its conjugate base.Stabilizers can be used alone or in combination and significantlydecrease the rate at which oxidizing agents such as hydrogen peroxidedecomposes.

Preferred stabilizers include phosphoric acid, phthalic acid, citricacid, adipic acid, oxalic acid, malonic acid, benzonitrile and mixturesthereof. The preferred stabilizers will be added to the compositions andslurries of this invention in an amount ranging from about 1 equivalentper catalyst to about 3.0 weight percent or more and preferably in anamount ranging from about 1 equivalent per catalyst to about 15equivalents per catalyst. As used herein, the term "equivalent percatalyst" means one molecule of stabilizer per catalyst ion in thecomposition. For example 2 equivalents per catalyst means two moleculesof stabilizer for each catalyst ion.

A more preferred stabilizer is from about 1 equivalents per catalyst toabout 15 equivalents per catalyst of malonic acid and most preferablyfrom about 1 to about 5 equivalents malonic acid.

The chemical mechanical polishing composition of this invention has beenfound to have a high tungsten (W) polishing rate as well as goodpolishing rates towards titanium (Ti). In addition, the chemicalmechanical polishing composition exhibits desirable low polishing ratestowards the dielectric insulating layer.

The composition of this invention may be produced using any techniquesknown to those skilled in the art. For example, the compound capable ofetching tungsten and the compound which acts to inhibit tungsten etchingmay be combined before applying the composition to a tungsten containingwafer or they may be independently applied to a polishing pad or to atungsten wafer before or during tungsten wafer polishing. Thecomposition of this invention may generally be manufactured by combiningthe ingredients together in any order.

In one method, for example, the compound capable of etching tungsten andtungsten etching inhibitor are mixed into an aqueous medium, such asdeionized or distilled water, at predetermined concentrations under lowshear conditions until such components are completely dissolved in themedium. A concentrated dispersion of the metal oxide abrasive, such asfumed silica, is optionally added to the medium and diluted to thedesired loading level of abrasive in the final CMP slurry. In addition,optional catalyst and other additives such as one or more stabilizers,may be added to the slurry by any method that is able to incorporatemetal catalytic compounds of this invention in an aqueous solution. Theresulting slurries are typically filtered to remove large contaminantssuch as hair, small stones and so forth from the slurry before it isused.

In another method, the stabilizer and catalyst are admixed to form acomplex prior to combining the complex with an oxidizing agent such ashydrogen peroxide. This may be accomplished by admixing the stabilizerand a metal oxide abrasive dispersion to give an abrasive/stabilizerdispersion followed by admixing the catalyst with theabrasive/stabilizer dispersion to give a catalyst/stabilizer complex ina metal oxide dispersion. The oxidizing agent is then added to theadmixture. When the metal oxide abrasive is alumina, then the stabilizerand catalyst should be admixed to form a complex prior to admixing thecomplex with the alumina abrasive, otherwise the catalyst may berendered ineffective.

Some inhibitors of tungsten etching may decompose in the presence ofhydrogen peroxide or other compositions capable of etching tungsten. Ifthere are compatibility problems between the inhibitor of tungstenetching and other compound ingredients, then the inhibitor should becombined with the other ingredients immediately before use.

The compositions of the present invention may be supplied as a onepackage system comprising at least a composition capable of etchingtungsten and an inhibitor of tungsten etching. Optional components, suchas an abrasive and any optional additives may be placed in either thefirst container, the second container or in a third container.Furthermore, the components in the first container or second containermay be in dry form while the components in the corresponding containerare in the form of an aqueous dispersion. For example, the firstcontainer may comprise an organic per compound such as hydrogenperoxide, in liquid form while the second container comprises aninhibitor of tungsten etching in dry form. Alternately, the firstcontainer may comprise a dry per compound or fluoride containingcompound while the second container may comprise an aqueous solution ofat least one inhibitor of tungsten etching. Other two-container, andthree or more container combinations of the ingredients of the chemicalmechanical composition and CMP slurry of this invention are within theknowledge of one of ordinary skill in the art.

EXAMPLES

We have discovered that a composition including a compound capable ofetching tungsten and an inhibitor of tungsten etching is capable ofpolishing a multiple metal layer comprising tungsten and titanium athigh controlled rates while exhibiting an acceptable low polishing ratetowards the dielectric layer.

The following examples illustrate preferred embodiments of thisinvention as well as preferred methods for using compositions of thisinvention.

Example 1

A chemical mechanical polishing slurry was prepared in order to evaluatethe ability of the resulting slurries to etch tungsten. A standard CMPslurry was prepared consisting of an aqueous solution of 5.3 wt %silica, 53 ppm iron in the form of ferric nitrate, 3.75 wt % H₂ O₂, and0.05 wt % malonic acid. The silica was predispersed before combining itwith the other slurry ingredients as described in Example 3.

Small uniform pieces of a tungsten wafer were immersed in the CMP slurryfor 30 minutes, recovered, dried, and the thickness measured byresistivity. The rate of tungsten etching was then calculated in unitsof A/min. The standard slurry exhibited a tungsten etching rate of 41Å/min.

0.04 wt % of compounds viewed as potential inhibitors of tungstenetching were added to the standard slurry after which the ability of theCMP slurry to etch tungsten was evaluated. The results of the etchingtests are reported in Table 1, below.

                  TABLE 1                                                         ______________________________________                                        Tungsten Etching Evaluation                                                                                   Rate                                          Slurry                                                                              Additive                  Ang/min                                       ______________________________________                                        1     None                      41                                            2     2,3,5-trimethylpyrazine   35                                            3     2-ethyl-3,5-dimethylpyazine                                                                             33                                            4     Quinoxaline               31                                            5     2-acetyl pyrrole          36                                            6     Pryridazine               31                                            7     Histidine                 6                                             8     Pyrazole                  48                                            9     5-nitroindazole           37                                            10    3,5-dimethylpyrazole      38                                            11    Pyrazine                  31                                            12    Benzimidazole             36                                            13    Benzotriazole             40                                            14    Pyridine                  45                                            15    monoquat isies (isostearylethylimididonium)                                                             1                                             16    cetyltrimethyl ammonium hydroxide                                                                       3                                             17    Alkaterge e (2-heptadecenyl-4-ethyl-2 oxazoline                                                         9                                                   4-methanol)                                                             18    aliquat 336 (tricaprylmethyl ammonium chloride)                                                         22                                            19    nuosept 101 (4,4 dimethyloxazolidine)                                                                   37                                            20    Tetrabutylammonium hydroxide                                                                            40                                            21    Tetramethylammonium hydroxide                                                                           40                                            22    Glutathione (reduced)     3                                             23    Cysteine                  6                                             24    2-mercapto benzimidazole  35                                            25    Cystine                   5                                             26    Thiophene                 40                                            27    mercapto pyridine n-oxide 39                                            28    thiamine hydrochloride    11                                            29    tetraethyl thiuram disulfide                                                                            39                                            30    2,5-dimercapto-1,3-thiadiazole                                                                          47                                            ______________________________________                                    

Example 2

Chemical mechanical polishing slurries including various inhibitors oftungsten etching were prepared in order to evaluate the ability ofvarious the resulting slurries to etch tungsten. A standard CMP slurrywas prepared consisting of an aqueous solution of 5.0 wt % silica. Thesilica was predispersed before combining it with the other slurryingredients as described in Example 3. The predispersed silica wascombined with 50 ppm iron in the form of ferric nitrate, 4 wt % H₂ O₂,and 3 equivalents malonic acid per atom of iron catalyst. The pH of theresulting slurry was adjusted to 2.3 with nitric acid. Small uniformpieces of tungsten wafer were immersed in the CMP slurry for 30 minutes,recovered, dried and the thickness measured by resistively. The rate oftungsten etching was then calculated in units Å/min. The standard slurryexhibited tungsten etching rate of 45 Å/min. Varying amounts ofinhibitors of tungsten etching were added to the standard slurry afterwhich the ability of the CMP slurry to etch tungsten was evaluatedidentically to the method used to evaluate the standard slurry tungstenetch rate. The result of the etching tests are reported in Table 2below.

                  TABLE 2                                                         ______________________________________                                        Sample    Formulation   Etch Rate (Å/min)                                 ______________________________________                                        31        None          45                                                    32        0.05% phenylalanine                                                                         29                                                    33        0.05% lysine  8                                                     34        0.05% tyrosine                                                                              26                                                    35        0.05% glutamine                                                                             11                                                    36        0.05% glutamic Acid                                                                         16                                                    37        0.05% glycine 14                                                    38        0.015% cystine                                                                              8                                                     ______________________________________                                    

A second base chemical mechanical polishing slurry was prepared. Theslurry consisted of 5.0 wt % fumed silica. The silica was predispersedbefore combining it with the other slurry ingredients as described inExample 3. The predispersed silica was combined with 50 ppm iron in theform of ferric nitrate, 0.05 wt % malonic acid, 4.0 wt % hydrogenperoxide, 0.001 wt % Kathon 866 MW bactericide manufactured by Rohm &Haas, and deionized water. The base slurry was adjusted with nitric acidto a pH of 2.3. The slurry was combined with various amino acids of thetype and amount set forth in Table 3, below. The slurry etch rate wasdetermined as described above.

                  TABLE 3                                                         ______________________________________                                        Sample   Formulation     Etch Rate (Å/min)                                ______________________________________                                        39       None            46                                                   40       0.04% cysteine  7                                                    41       0.05% cystine   5                                                    42       0.05% serine    21                                                   43       0.05% 3,3-dithiopropionic                                                                     40                                                            acid                                                                 44       0.06% 2,5-diphenyl-1,6,6a-                                                                    36                                                            trihiapentane                                                        ______________________________________                                    

These results show that slurries containing compounds including thiolsor disulfides in combination with a nitrogen containing functional groupare effective at reducing tungsten etching.

Example 3

A polishing slurry was prepared in order to evaluate its performance ontungsten wafer CMP. Performance parameters measured included tungstenpolishing rates. A standard abrasive slurry including 5.0 weight percentfumed silica was prepared. The slurry was prepared by predispersingsilica, having a surface area of 150 m² /g under high shear to make aconcentrated dispersion. The dispersion was then filtered sequentiallywith a 5 micron bag filter, followed by a 1 micron bag filter, followedby a 1 micron cartridge filter, and finally with a 0.2 micron cartridgefilter before diluting the silica further and adding the remainingingredients. The remaining slurry ingredients included 0.036 wt % ironcatalyst in the form of ferric nitrate nonahydrate, 6.0 weight percentof hydrogen peroxide, 0.05 weight percent malonic acid and deionizedwater with 0.05 wt % pyridazine added as a tungsten corrosion inhibitor.The pH of the final slurry was adjusted to 2.3 with nitric acid.

The CMP slurry was applied to chemically-mechanically polish a tungstenpatterned wafer having thickness of approximately 8000 Å of tungstenusing a SUBA500/SUBAIV pad stack manufactured by Rodel, Inc. Thepolishing was performed using a IPEC 472 tool at a down force of 5 psi,a slurry flow rate of 150 ml/min, a table speed of 60 rpm, and a spindlespeed of 65 rpm.

Without the pyridazine tungsten corrosion inhibitor, the CMP slurryexhibited tungsten plug recessing of about 350 Å on a 0.5 micrometerplug. The addition of 0.05 wt % pyridazine tungsten corrosion inhibitordecreased tungsten plug recessing to about 230 Å without any loss inother polishing performance characteristics such as rate, uniformity anderosion.

Example 4

A base slurry was prepared for this example. The base slurry included 5wt % fumed silica, 50 ppm iron in the form of ferric nitrate, 2.0 wt %hydrogen peroxide, 0.05 wt % malonic acid, 0.001 Wt % Kathon in water.The silica was predispersed before combining it with the other slurryingredients as described in Example 3. After addition of additivesidentified in Table 4, the pH was adjusted, as necessary, to theindicated pH using nitric acid or potassium hydroxide. The etch rates ofeach slurry were determined following the method described in Example 2.

                  TABLE 4                                                         ______________________________________                                        Slurry Additive          pH     W Rate Ang/min                                ______________________________________                                        45     None              2.3    29                                            46     0.02% oxalic acid 2.3    98                                            47     0.02% oxalic acid + 0.05%                                                                       2.3    45                                                   glycine                                                                48     0.05% dodecylamine                                                                              2.3    0                                             49     0.03% Silquest A-1106                                                                           2.3    1                                             50     None              5.0    64                                            51     0.05% glycine     5.0    47                                            52     None              7.0    124                                           53     0.05% glycine     7.0    101                                           54     0.03% Silquest A-1106                                                                           7.0    85                                            ______________________________________                                    

The results from Table 4 show that the tungsten etch rate increase uponaddition of an organic acid, oxalic acid, to slurry 46. However, uponthe addition of glycine, a compound including a nitrogen functionalgroup to an oxalic acid containing slurry, the tungsten corrosion ratedropped. The addition of compounds including one or more amino alkylfunctional group such as dodecylamine, glycine and A-1106 alsosignificantly reduced the tungsten corrosion rate in comparison toslurries that do not contain an amino alkyl functional group. Finally,the results in Table 4 show that the compounds including the nitrogencontaining functional groups are able to inhibit tungsten etching to pHsat least as high as 7.0.

What we claim is:
 1. A chemical mechanical polishing compositioncomprising:a compound that is capable of etching tungsten; and at leastone inhibitor of tungsten etching, wherein the inhibitor of tungstenetching is a compound that includes a nitrogen containing functionalgroup selected from compounds having three or more carbon atoms thatform alkylammonium ions, amino alkyls having three or more carbon atoms,amino acids other than sulfur containing amino acids and mixturesthereof.
 2. The chemical mechanical composition of claim 1 wherein thecompound that includes a nitrogen containing functional group is acompound that forms di- tri- and tetraalkylammonium ions at a pH lessthan about
 9. 3. The chemical mechanical composition of claim 1 whereinthe inhibitor of tungsten etching is selected from naturally occurringamino acids that do not include a sulfur atom, synthetic amino acidsthat do not include a sulfur atom, and mixtures thereof.
 4. The chemicalmechanical composition of claim 1 wherein the inhibitor of tungstenetching is glycine.
 5. The chemical mechanical composition of claim 1wherein the inhibitor of tungsten etching is at least one compoundhaving three or more carbon atoms that forms alkylammonium ions in anaqueous solution having a pH less than about 5.0.
 6. The chemicalmechanical composition of claim 1 wherein the inhibitor of tungstenetching is aminopropylsilanol, aminopropylsiloxane, and mixturesthereof.
 7. The chemical mechanical polishing composition of claim 1wherein the compound capable of etching tungsten is at least oneoxidizing agent.
 8. The chemical mechanical polishing composition ofclaim 7 wherein the oxidizing agent is at least one per-compound.
 9. Thechemical mechanical polishing composition of claim 8 wherein theperoxide compound is hydrogen peroxide.
 10. The chemical mechanicalpolishing composition of claim 9 including from about 0.1 to about 50weight percent hydrogen peroxide.
 11. The chemical mechanical polishingcomposition of claim 9 including from about 0.5 to about 10 weightpercent hydrogen peroxide.
 12. The chemical mechanical polishingcomposition of claim 1 wherein the compound capable of etching tungstenis at least one fluoride containing compound.
 13. The chemicalmechanical polishing composition of claim 1 further comprising at leastone metal catalyst, wherein the compound capable of etching tungsten isan oxidizing agent.
 14. The chemical mechanical polishing composition ofclaim 13 wherein the metal catalyst is an iron catalyst selected fromthe group consisting of inorganic iron compounds and organic ironcompounds having multiple oxidation states.
 15. The chemical mechanicalpolishing composition of claim 14 wherein the iron catalyst is ferricnitrate.
 16. The chemical mechanical polishing composition of claim 15including from about 0.001 to about 2.0 weight percent ferric nitrate.17. The chemical mechanical polishing composition of claim 1 wherein thecompound capable of etching tungsten is hydrogen peroxide and whereinthe composition further includes from about 0.001 to about 0.2 weightpercent of an iron catalyst.
 18. A chemical mechanical polishing slurryincluding the chemical mechanical composition of claim 1 and at leastone metal oxide abrasive.
 19. The chemical mechanical polishing slurryof claim 18 wherein the metal oxide abrasive is selected from the groupincluding alumina, ceria, germania, silica, titania, zirconia, andmixtures thereof.
 20. The chemical mechanical polishing slurry of claim18 wherein the metal oxide abrasive is an aqueous dispersion of a metaloxide.
 21. The chemical mechanical polishing slurry of claim 20 whereinthe metal oxide abrasive consists of metal oxide aggregates having asize distribution less than about 1.0 micron and a mean aggregatediameter less than about 0.4 micron.
 22. The chemical mechanicalpolishing slurry of claim 18 wherein the metal oxide abrasive consistsof discrete, individual metal oxide spheres having a primary particlediameter less than 0.400 micron and a surface area ranging from about 10m² /g to about 250 m² /g.
 23. The chemical mechanical polishing slurryof claim 18 wherein the metal oxide abrasive has a surface area rangingfrom about 5 m² /g to about 430 m² /g.
 24. The chemical mechanicalpolishing slurry of claim 23 wherein the metal oxide abrasive has asurface area of from about 30 m² /g to about 170 m² /g.
 25. The chemicalmechanical polishing slurry of claim 18 wherein the metal oxide abrasiveis a precipitated abrasive or a fumed abrasive.
 26. The chemicalmechanical polishing slurry of claim 18 wherein the metal oxide abrasiveis silica.
 27. The chemical mechanical polishing slurry of claim 26wherein the silica is fumed silica.
 28. The chemical mechanicalcomposition of claim 1 including at least one stabilizer.
 29. Thechemical mechanical composition of claim 1 including at least onestabilizer selected from phosphoric acid, phthalic acid, citric acid,adipic acid, oxalic acid, malonic acid, benzonitrile and mixturesthereof.
 30. The chemical mechanical polishing composition of claim 28wherein the stabilizer is from about 1 equivalents per catalyst to about15 equivalents per catalyst of malonic acid.
 31. A chemical mechanicalpolishing slurry comprising:from about 0.5 to about 15.0 weight percentsilica; from about 0.001 to about 0.2 weight percent ferric nitratecatalyst; from about 0.5 to about 10.0 weight percent hydrogen peroxide;at least one stabilizer; andfrom about 0.001 to about 1.0 wt % of aninhibitor to tungsten etching selected from glycine, aminopropylsilanol,aminopropylsiloxane, and mixtures thereof, wherein the slurry has a pHless than about
 9. 32. The chemical mechanical polishing slurry of claim31 wherein the inhibitor of tungsten etching is glycine.
 33. Thechemical mechanical polishing slurry of claim 31 wherein the inhibitorof tungsten etching is the mixture of glycine, aminopropylsilanol, andaminopropylsiloxane.
 34. The chemical mechanical polishing slurry ofclaim 31 wherein the stabilizer is from about 1 to about 5 equivalentsper catalyst of malonic acid.
 35. A method for polishing a substrateincluding at least one tungsten layer comprising the steps of:(a)admixing at least one compound that is capable of etching tungsten, atleast one inhibitor of tungsten etching and deionized water to give achemical mechanical polishing composition having a pH less than 9.0,wherein the inhibitor of tungsten etching is an amino alkyl having threeor more carbon atoms, compounds having three or more carbon atoms thatform alkylammonium ions at a solution pH less than about 9.0, aminoacids other than sulfur-containing amino acids, and mixtures thereof;(b) applying the chemical mechanical polishing composition to thesubstrate; and (c) removing at least a portion of the tungsten layerfrom the substrate by bringing a pad into contact with the substrate andmoving the pad in relation to the substrate.
 36. The method of claim 35wherein the substrate further includes a titanium and/or titaniumnitride metal layer wherein at least a portion of the titanium nitridelayer is removed in step (c).
 37. The method of claim 35 wherein thecompound capable of etching tungsten is hydrogen peroxide.
 38. Themethod of claim 35 wherein the chemical mechanical composition includesa catalyst selected from the group inorganic iron compounds and organiciron compounds.
 39. The method of claim 38 wherein the catalyst is fromabout 0.001 to about 2.0 weight percent ferric nitrate.
 40. The methodof claim 35 wherein the chemical mechanical composition includes atleast one metal oxide abrasive to give a chemical mechanical polishingslurry.
 41. The method of claim 40 wherein the metal oxide abrasive isselected from the group including alumina, ceria, germania, silica,titania, zirconia, and mixtures thereof.
 42. The method of claim 40wherein the metal oxide abrasive is an aqueous dispersion of a metaloxide.
 43. Thc method of claim 40 wherein the metal oxide abrasive isselected from the group consisting of precipitated alumina, fumedalumina, precipitated silica, fumed silica, and mixtures thereof. 44.The method of claim 40 wherein the metal oxide abrasive is from about0.5 to about 15.0 weight percent silica.
 45. The method of claim 35wherein the inhibitor of tungsten is selected from the group naturallyoccurring amino acids that do not include sulfur, synthetic amino acidsthat do not include sulfur, and mixtures thereof.
 46. The method ofclaim 35 wherein the inhibitor of tungsten etching is glycine.
 47. Themethod of claim 35 wherein the inhibitor of tungsten etching is at leastone compound that forms tetraalkylammonium ions in an aqueous solutionhaving a pH less than about 5.0.
 48. The method of claim 47 wherein theinhibitor of tungsten etching is selected from glycine,aminopropylsilanol, aminopropylsiloxane, and mixtures thereof.
 49. Amethod for polishing a substrate including tungsten layer comprising:(a)admixing from about 0.5 to about 15.0 weight percent silica, from about0.001 to about 0.2 weight percent ferric nitrate catalyst, from about0.5 to about 10.0 weight percent hydrogen peroxide, at least onestabilizer; and from about 0.001 to about 1.0 wt % glycine, anddeionized water to give a mechanical chemical polishing slurry having apH of from about 2.0 to about 5.0; (b) applying the chemical mechanicalpolishing slurry to the substrate; and (c) removing at least a portionof the tungsten layer by bringing a pad into contact with the substrateand moving the pad in relation to the substrate.
 50. The method of claim49 wherein the chemical mechanical polishing slurry includesaminopropylsilanol and aminopropylsiloxane.
 51. The chemical mechanicalpolishing composition of claim 1 wherein the inhibitor of tungstenetching is from about 0.01 to about 0.1 wt % glycine.
 52. The chemicalmechanical polishing composition of claim 1 wherein the inhibitor oftungsten etching is selected from isosterylethylimididonium, cetytrimethylamminium hydroxide, 2-heptadecenyl-4-ethyl-2 oxazoline4-methanol, 4,4 dimethyloxazolidine, phenylalamine, lysine, tyrosine,glutamine, glutamic acid, histidine, cystine, dodecylamine, and mixturesthereof.